Fixed-bed reactors packed with catalysts are often used in chemical plants, oil refineries, and other facilities where catalytic reactions are performed. In such fixed-bed reactors, the spaces between the catalyst particles tend to be plugged by the granular substances transported by fluids (starting materials for the reactions) or by the granular substances formed as reaction by-products, making it impossible to perform the desired catalytic reactions.
In conventional practice, such catalyst plugging is prevented by packing the top portion of a reactor (upstream portion or the area near the inlet for the feed stocks of the reaction) or the entire reactor with highly porous pipe-shaped catalysts (so-called Raschig ring catalysts) or catalysts having a trefoil or quatrefoil shape in cross section. These catalysts are commonly manufactured by supporting metal components on catalyst carriers that have been extrusion-shaped to the desired shape. Another widely used method of preventing catalyst plugging is so-called size grading, according to which a reactor is packed with catalysts such that the catalyst size gradually decreases in the direction from the upstream to the downstream of the reactor.
For example, Japanese Patent Application Laid-open No. 6-198185 discloses a hydrodesulfurization catalyst shaped and baked such that the catalyst diameter/catalyst length ratio is kept within a range of 1:1 to 1:3 in order to reduce the pressure loss of the feed stock components passing through the catalyst, and reduce the bulk density of the catalyst.
Variously shaped catalyst pellets are also disclosed in "Selecting the Catalyst Configuration" (Chemical Engineering, May 12, 1986; pp. 97-101). Described in this report is the relation between the pressure loss or efficiency of a catalyst and the inner/outer diameter ratio of hollow pellets.
In addition, catalysts provided with cylindrical, trefoil, cinquefoil, annular, and other configurations and used for the hydrogenation of heavy oil are disclosed in the Technology section of Oil & Gas Journal (Dec. 8, 1986; pp. 39-44), and the effect of these configurations on the pressure loss or catalytic activity is discussed.
The inventors believe, however, that conventional catalysts shaped with the aim of achieving increased porosity in the above-described manner cause reaction fluids to undergo channeling when these reaction fluids pass through the catalysts. Such channeling is primarily attributed to the following three factors. First, a Raschig ring catalyst or an extrusion-formed catalyst having a trefoil or quatrefoil cross-sectional shape makes it easier for fluids to flow in the longitudinal direction of the catalyst. Second, common packing methods in which the catalyst is packed into a reactor without being oriented in a specific direction are characterized by the fact that the longitudinal direction of the packed catalysts tends to be partially aligned in a specific direction. When channeling occurs, only that portion of the catalyst packed into the reactor through which the reaction fluid passes can be efficiently used, resulting in lower catalytic reaction efficiency. In addition, hot spots are formed in the catalyst when the catalytic reaction is highly exothermic, and coke is produced by pyrolysis (sometimes resulting in so-called coking) when the reaction fluid is heavy oil.
In addition, the aforementioned size grading is disadvantageous in that because the catalyst size must gradually increase in the upstream direction of the catalyst layer, catalytic activity decreases and catalyst life is reduced when reactions in which the diffusion of reactants into catalyst pores is the rate determining step of the reaction process occur upstream of the catalyst layer or reactor (for example, in the case of a hydrodemetallation reaction involving heavy oil).
An object of the present invention, which was achieved in order to overcome the above-described shortcomings of conventional method and catalyst, is to provide a catalyst carrier, a catalyst obtained using this carrier and a hydrogenation reactor, which are capable of reducing the channeling of the reaction fluid in the reactor.
Another object of the present invention is to provide a catalyst carrier that makes it less likely that the catalyst will be plugged by the granular substance in the reaction fluid and that allows high catalytic activity to be maintained for a long time, to provide a catalyst obtained using this carrier, and to provide a fixed-bed reactor packed with this catalyst.
Yet another object of the present invention is to provide a catalytic reaction method that allows reactions to be performed without lowering the catalytic reaction efficiency as a result of catalyst plugging even in the case of a reaction fluid containing granular substances.